In general, infrared radiation (IR) sensors are used in a variety of applications to detect infrared radiation and provide an electrical output that is a measure of the incident infrared radiation. One type of infrared sensor is a bolometer. A bolometer typically includes an absorber element for absorbing infrared radiation and a transducer element that has an electrical resistance that varies with temperature. In operation, infrared radiation incident upon the bolometer is absorbed by the absorber element and transferred to the transducer element in the form of heat. The heat causes the electrical resistance of the transducer element to change in a manner that is proportional to the amount of infrared radiation incident on the absorber element. Therefore, by detecting changes in the electrical resistance, a measure of the incident infrared radiation can be obtained.
Heat transference between the absorber element and the substrate can result in heat losses and heat gains that can adversely impact the reliability and accuracy of the sensor. To minimize heat losses and heat gains, the absorber element and transducer element are typically incorporated into a suspension structure that is suspended above the surface of the substrate. By suspending the absorber element above the substrate, the possibilities of heat transference due to thermal contact with the substrate are minimized.
The reliability and accuracy of bolometer sensors may also be impacted by process variations and drift of material properties and other factors over time. Bolometer sensors also face the problem of Joule-heating. Joule-heating results when an electric current is passed through the transducer element to detect heat induced changes in the electrical resistance. The electric current generates heat in the transducer element which increases the temperature of the transducer element beyond the temperature resulting from heat transference from the absorber element.
Process variations, drift, Joule-heating, and other similar factors can introduce variations, such as drift and offset, into sensor output. Compensation values are often incorporated into the sensor output to compensate for deviations in sensor output due to drift and offset. The compensation values, however, are typically based on historical performance and test data from other sensors.